A. Field of the Invention
The present invention relates generally to an attachment system for use with optical technology based displacement detection, and more particularly, to an attachment system for use with optical technology in an input device.
B. Description of the Related Art
Optical technology displacement detection is used in many contexts, including in optical input devices. There are many different types of input devices, including a mouse, a trackball, a joystick, and a digital pen. There are significant advantages to using optical input devices over mechanical and opto-mechanical input devices. For example, mechanical or opto-mechanical input devices have mechanical components that are more susceptible to breakdown, wear out, or clogging. Optical devices having only solid-state components are less susceptible to such breakdown, dirt, or wear out.
Optical input devices use a displacement of an image to detect movement of the input device relative to a surface, e.g., a table surface in the case of a mouse or a ball in the case of a trackball. Optical input devices use an illumination lens, an imaging lens, a sensor, and a light source to detect movement of the input device. Typically the light source is a light emitting diode (LED). The LED is usually attached with a conventional clip to a printed circuit board (PCB). The sensor is mounted on the PCB. The sensor is attached to the imaging lens. The conventional clip is not a precise clip. For example, if the PCB becomes warped or bent, the conventional clip will be holding the LED in place, but not in an optimum place. The LED package dimensions have large tolerances. These dimension errors also degrade the alignment of the LED.
Now referring to FIG. 1, there is shown an overview of a prior art attachment system. FIG. 1 shows an optical system 105, an optical illumination lens 115, a light source 100, a conventional clip 120, a PCB 125, and a sensor 130. The conventional clip 120 is attached to the PCB 125. The sensor 130 is mounted on the PCB 125. The sensor 130 is attached to the imaging lens.
A mechanical assembly for attaching the LED (the conventional clip) and its alignment with the illumination lens, imaging lens, and the sensor is critical to efficient performance of the optical device. The LED alignment has a direct impact on the surface illumination and therefore on image quality. Good surface illumination and good image quality is essential to an efficient optical system in an input device. A surface illumination has an illumination spot with a predetermined amount of energy, distributed as evenly as possible, and in alignment with the imaging lens. It also makes the device less sensitive to “difficult” surfaces. A “difficult” surface is one on which the optical device does not detect displacement very well, for example, a dark surface or a glossy surface. There are several reasons the alignment is not always good. One reason is the attachment system.
There are several main problems with conventional attachment systems. One problem with conventional systems is the illumination of the imaged area analyzed by the sensor. This problem results from the fact that the LED is not correctly and precisely positioned with respect to the illumination system. Thus, the illumination spot, the area actually lighted by the illumination system, is shifted relative to the imaged area. One solution conventional systems have employed to overcome this problem is to make the illumination spot much larger than the imaged area. However, this solution is inefficient because it wastes light, which translates to a waste of power.
Also, in conventional systems the LED is mounted on the PCB using a conventional clip. The PCB is coupled to the sensor, which is coupled to the illumination lens. The illumination lens is coupled to the imaging lens. Thus, the coupling between the LED and the illumination lens is dependent on the integrity of the conventional clip, the PCB, and the sensor. The conventional clip is a cylindrical tube, which holds the LED in place. However, due to large play required to accommodate the LED dimension errors, the LED can wiggle or wobble in the cylindrical tube causing positional errors in the light beam.
What is needed is an attachment system for use in an optical system that overcomes the above described problems and limitations of precise positioning of the light source relative to the illumination system.